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"A penny for your thoughts"

Monday, September 1, 2008

In Kenya slum, generating energy from human waste, sun used to purify water

Just 48 hours of sunlight can kill germs that cause cholera, typhoid, and other diseases—a discovery that's already helping Kenya's poor.
August 24, 2008
NAIROBI, Kenya -
People in Nairobi's Kibera slum are surviving soaring food and fuel prices and poor sanitation by harnessing the power of two things they have in plenty: sewage and sunshine. Some have helped construct a network of public latrines that recycle human waste into gas for cooking and light. Others, assisted by a Swiss aid organization, use sunlight to purify drinking water, dramatically slashing cases of waterborne disease.Solar Water Disinfection

For up to a million residents in Kibera, it's harder than ever to scrape together a dollar for cornflour and wilted cabbage for one meal a day. Staple food prices in the capital have doubled in six months. And the price of coal for cooking has increased by a quarter.The "bio-latrines" are built next to a school for orphans. Around 600 people use them, generating enough gas to cook for 68 orphans next door and provide hot water for a shower block serving hundreds of people.

The project, adapted from a design produced in Tanzania, is funded by an alliance of international donors and run by the communities themselves.

Residents pay three cents to use one of eight drop toilets installed around a buried tank. The waste goes into an airtight "biodigester," where methane gas filters into an upper tank. The gas can be used to light stoves, turn on lamps, or heat water, although it is not yet pumped to individual homes.

The biogas plant consists of two components: a digester (or fermentation tank) and a gas holder. The digester is a cube-shaped or cylindrical waterproof container with an inlet into which the fermentable mixture is introduced in the form of a liquid slurry. The gas holder is normally an airproof steel container that, by floating like a ball on the fermentation mix, cuts off air to the digester (anaerobiosis) and collects the gas generated. In one of the most widely used designs (Figure above), the gas holder is equipped with a gas outlet, while the digester is provided with an overflow pipe to lead the sludge out into a drainage pit.

Solid waste is treated and filtered through reed beds before being collected to be sold as fertilizer.The first center built four years ago in Kibera proved so successful that there are now 34 other bio-gas projects in various stages of completion around Kenya. If another 200 people a day came to spend a few pennies on use the drop toilets, there would be enough gas to light a street lamp in this slum where there has never been electricity. That would mean safer streets in a part of town where glue-sniffing gangsters lurk in the alleys after dark.

One big benefit of the bio-latrines is the fall in what residents call "flying toilets" — plastic bags that slum residents sometimes use to relieve themselves and then fling out of shack doors into alleys, occasionally catching unwary passers-by.
But not everyone in the slums has a bio-latrine nearby. Often, trickles of sewage in the streets become streams choked with garbage, used condoms and rotting food. Bedraggled puppies splash in the waste. These rivers of disease often run parallel with cracked, corroded pipes bringing water to communal taps. Germs enter the water supply through the leaks, sickening children whose parents cannot afford doctor fees.

That's where Kaltouma Tahir and her water purification project come in to help start a pilot project run by the Swiss aid organization that purifies water using the sun's ultraviolet rays. Now she shows each neighbor how to place clear plastic bottles with the contaminated piped water onto corrugated metal roofs. The one liter bottles only cost a few cents each and are reusable.

The 52-year-old mother neighbor's 3-year-old son Gilbert get sick and die after contracting diarrhea from drinking dirty water seven years ago still linger in her mind.She says in the seven years since the program was launched, deaths of neighborhood children from waterborne diseases have fallen from about 20 per year to two or three. Tests conducted in Swiss labs showed six hours in the sunshine or two days if it's overcast is enough light to kill off almost all germs that cause diseases, including cholera, typhoid, dysentery, polio and hepatitis.

Kenyan chemist David Kariuki says that in areas where the project has taken off, local clinics have seen a 90 percent reduction in the number of patients with waterborne diseases. Children don't miss school and parents don't miss work. Savings that would have gone to medicine are spent on school books or extra food instead.
Related Post: Turning animal/Human waste into energy

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A Rwandan prison project, which reduces cooking fuel bills by using methane gas from inmates' toilet waste, has won a global environment award.

Biogas Introduction

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